The invention relates to a device for operation of a motor vehicle engine at idle speed. The engine includes two rows of cylinders, with a catalytic converter and oxygen sensor associated with each row. The invention also relates to a device for control of a motor vehicle engine with a catalytic converter and an oxygen sensor operating at idle speed.
A device is already known for turning off the motor vehicle's engine while it is stopped, even during a brief stop by the motor vehicle. This known device is frequently referred to as a "start-stop automatic." With this "start-stop automatic," all of the cylinders of the engine are switched off when the engine is shut-off. This has the disadvantage that the catalytic converter or converters of the engine cools very rapidly and, consequently, after the engine is started, the catalytic converter must be brought back to the necessary conversion temperature by appropriately enriching the intake mixture of the engine. However, the enriching of the mixture has a negative effect on exhaust emissions and on fuel consumption.
On the other hand, when the engine is operated with the vehicle at rest at idle, with all of the cylinders firing, critical thermal behavior can result if the amount of heat generated by combustion cannot be carried away by the coolant for lack of an air stream, particularly in large-volume multicylinder engines.
Therefore, there is needed to provide a device of the above-described type by which the fuel consumption of the engine at idle speed is reduced, while still retaining the exhaust quality. Consequently, the thermal behavior of the engine is improved.
These needs are met according to the present invention in a first embodiment of a device for idle control of a vehicle engine having two rows of cylinders, a catalytic converter and an oxygen probe associated with each row, by virtue of the fact that during operation of the engine at idle the injectors of one of the two rows of cylinders are alternately shut-off and the injector shut-off is switched from one row of cylinders to the other when the temperature of the catalytic converter associated with the row of cylinders that has just been shut-off falls below a preset temperature limit.
This first embodiment of the invention is especially suitable for eight- to twelve-cylinder internal combustion engines having a v-shaped arrangement of cylinders. The arrangement can consist of two four-cylinder or two six-cylinder engines depending on their firing order. Especially in a twelve-cylinder internal combustion engine of this design, no significant deterioration of idle quality occurs because of the complete balancing of masses of a row of cylinders.
According to a second embodiment of the present invention, the needs are met by a device for control of a motor vehicle engine at idle with a catalytic converter and oxygen sensor. During operation of the engine at idle, the injectors are switched off sequentially as a function of the engine firing order according to a fixed program, and the sequential injector shut-off is suspended at least for a specified period of time if the temperature of the catalytic converter falls below a preset temperature limit.
This second embodiment of the invention is also suitable for six-cylinder engines.
Each of the two embodiments of the present invention ensures that the catalytic converter or converters cannot cool below the temperature required for proper exhaust conversion. This results in improved engine exhaust emissions. Consequently, by shutting-off individual cylinders when the engine is idling, its fuel consumption at idle can be reduced by about 35%. Finally, the thermal behavior, especially in large volume engines at idle, when the cooling effect of the air stream is absent, is definitely improved by the present invention.
It is a further advantage of the present invention that the sequential shut-off of the injectors or the alternate switching of the injectors of one row of cylinders during operation of the engine at idle takes place only when the coolant temperature of the engine is above 80.degree. C. and/or the air temperature in the intake manifold is above 20.degree. C. This ensures that individual cylinder shut-off at idle operation of the engine takes place only when the engine is at operating temperature and/or the outside temperature is sufficiently warm.
In order to avoid an unpleasant torque surge at the output from the engine when parking or slowly coasting, according to another embodiment of the invention, the sequential shut-off of the injectors or the alternate shut-off of the injectors in one row of cylinders is suspended when the vehicle speed exceeds 5 km/h.
In another advantageous embodiment of the invention, the temperature of the catalytic converter or converters is determined by measuring or monitoring the electrical voltage of the oxygen sensor associated with the catalytic converter in question.
The two embodiments of the present invention will now be described with reference to an embodiment of each.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.